Modern electrical power distribution systems supply power to a large number of electrical loads, such as residences, factories or businesses. The power consumed by each electrical load is separately measured by an electrical metering device, such as an induction or electronic type watthour meter. Many electrical power distribution systems include tens of thousands, hundreds of thousands or more metering devices.
Induction type watthour meters have historically been utilized to measure electrical energy consumption. Recently, however, an increasing number of electrical metering devices, such as electronic type watthour meters, have been employed to measure electrical energy consumption. The use of electronic type watthour meters has increased, in part, since electronic meters can measure several quantities in addition to tabulating the kilowatt hours of power consumed by the corresponding load. In addition, electronic type watthour meters may be reprogrammed to alter their operation once they have been installed so as to offer additional metering flexibility.
In order to "read" the electrical metering device to determine the power consumption of the associated load or to reprogram the electrical metering device, various methods of communicating with electrical metering devices have been employed. According to one method of communicating with electronic type watthour meters, a display associated with the meter is observed. Alternatively, the signals may be optically transmitted to and received from an electronic type watthour meter having an optical port using a corresponding optical probe. Both communications methods, however, require the meter to be physically visited in the field.
Since modern electrical power distribution systems include tens of thousands, hundreds of thousands or more metering devices, a power line communications method has been employed to transfer signals to and receive signals from electronic type watthour meters without having to physically visit the meter in the field. Many different types of signals may be transmitted including signals indicative of the quantities measured by the metering device, such as kilowatt hours of power consumed, so as to permit the meter to be "read" from a remote location. The signals may also include revised instructions to reprogram the electronic meter.
One power line communications system is the UCNet.TM. system marketed by General Electric Company, assignee of the present invention. The UCNet.TM. system is described and illustrated in a publication entitled "GE UCNet System" by GE Meter and Control of Somersworth, N.H., which bears document number GEA12091 9/91 7M. The UCNet.TM. system is also described in a publication entitled "Engineering Presentation to AEIC/EEI Meter and Service Committees" by GE Meter and Control which bears document number GET-6638.22 9/91 (3M). The disclosures of both publications are incorporated herein by reference.
A typical power line communications system, such as that illustrated in U.S. Pat. No. 4,749,992 to Fitzemeyer which is incorporated herein by reference, includes a central control station, typically referred to as a system control center, which transmits signals to one or more radio towers. The signals may be transmitted to the radio tower by RF transmission or by cable television or telephone lines or by a satellite or microwave link. Each radio tower, in turn, rebroadcasts the signals to a plurality of nodes, such as by RF transmission.
Each node is typically a remote local relay module associated with a distribution transformer. Each relay module then transmits the signals to the individual, electrical metering devices via the power lines which connect the associated distribution transformer to the metering devices. Thus, the power lines, in addition to transferring electrical power to the metering device and the electrical load, also act as a communications bus for communications between the node and the metering devices. Accordingly, a local area network is established between a node and the electrical metering devices operably connected to the secondary side of the distribution transformer associated with the node.
A power line communications system, such as the UCNet.TM. system, not only includes the power lines extending from the distribution transformer to the electrical loads, i.e. residences or businesses, but also the electrical wiring within the residences or businesses. The UCNet.TM. and other systems transmit signals via the power lines according to a predetermined format or protocol such as the consumer electronics bus ("CEBus") protocol. The CEBus protocol for power line signals is described in an interim standard published by the Electronic Industries Association of Washington, D.C. which is entitled "EIA Home Automation System (CEBus)", the contents of which are incorporated herein by reference.
Electronic type watthour meters coupled to the electrical loads of the distribution transformer include a modem for receiving and translating the signals transmitted via the power lines. The modem thereafter provides the translated signal to the controller or processor of the electronic type watthour meter. The modem is bidirectional so as to also transmit signals from the electronic type watthour meter on the power lines.
The node and each electronic type watthour meter within a local area network is assigned a predetermined address. As explained in more detail in the publication entitled "EIA IS-60 CEBus Volume 4 Node Protocol Draft Standard", the standard CEBus protocol includes seven hierarchical layers. The data link layer includes fields for the actual command or signal to be transmitted, designated the information field, as well as fields for the source address and the destination address of the signal. Accordingly, the device which sent and the device which is to receive the signal are identified by their respective predefined addresses.
Recently, an increasing number of electronic type watthour meters have been employed to measure electrical energy consumption since they can compute several quantities in addition to measuring the kilowatt hours of power consumed by the corresponding load. For example, electronic type watthour meters can compute the power factor, kilovolt amperes ("KVA"), and reactive volt amperes of power consumed by the corresponding load. The computation of the various measures of power consumption, such as power factor, KVA and reactive volt amperes of power consumed by each load of the power distribution system, is desirable since these measurements provide additional information regarding the customers' electrical energy usage. This information can be used by the power distribution company to more accurately anticipate the customers' future power demands and to plan accordingly.
The total electrical power demand upon most power distribution systems is cyclical throughout each day with one or more peaks in the demand for electrical energy. The cyclical electrical energy demand is relatively consistent such that the peaks in electrical energy demand occur at substantially the same time each day. Likewise, the off-peak time periods also occur at relatively the same times of each day. Thus, many suppliers of electrical power charge more for electrical energy consumption during the peak periods than during the off-peak periods to reflect the increased cost of supplying the power during the peak periods.
Electronic type watthour meters may also include an electronic register which can provide time of use metering as well as other functions. Time of use metering separately tabulates the electrical consumption of the load during distinct, predetermined periods of time. Electronic time of use watthour meters having electronic registers, therefore, may measure the electrical energy consumption separately during the predetermined off-peak and peak periods of time. Separate billing rates may thereafter be applied to the electrical consumption during those periods of time by the suppliers of the electrical power.
The increased metering flexibility and capacity provided by electronic type watthour meters is due, at least in part, to the electronic acquisition, integration and processing of the measured electrical consumption of the load. Within each electronic type watthour meter, the electronic processing is principally provided by the register. The register typically includes an electronic processor or controller as well as memory for data storage.
Electronic type watthour meters which measure several quantities, in addition to the kilowatt hours of power consumed by the associated load, typically require a fairly sophisticated register. For example, such a register may require a more advanced electronic processor or controller as well as additional memory for storing the computed quantities. In addition, the processor or controller of a sophisticated register may need to perform more rapid numerical processing in order to perform the necessary computations. The need for a sophisticated register is particularly apparent in electronic type watthour meters which provide time of use metering. In these registers, the necessary electronic processor or controller must perform all the necessary computations while, simultaneously, separating the power consumption among the distinct, predetermined periods of time.
Electronic type watthour meters which compute several measures of power consumption also generally include a comparatively sophisticated display adapted to display each of the computed measures of power consumption. The meter may thus be "read" upon physically visiting the meter.
Presently, each electronic type watthour meter of the electrical power distribution system includes a register. A significant and increasing number of these electronic type watthour meters incorporate relatively sophisticated registers to measure and calculate several quantities in addition to kilowatt hours of power consumed and to provide time of use metering. Thus, tens of thousands, hundreds of thousands or more of electronic metering devices incorporating sophisticated registers may be "in the field" as part of a modern electrical power distribution system.
Each electronic type watthour meter incorporating a sophisticated register is significantly more expensive than an electronic type watthour meter which includes a relatively simple register, such as an interval recording meter. However, it is desirable to continue to compute the additional measures of power consumption and to perform time of use metering which electronic type watthour meters having relatively sophisticated registers presently provide.